Chaos-Fixing the broken
by Dorian Havilliard
Summary: A crossover of TMI and HoO. Clary mistakenly opens a rune to another realm. Percy and Annabeth are having post Tartarus trauma. Chaos, the creator of the universe is going to try and fix them but not without them saving the world first.. as usual
1. Chapter 1

**Hope you like it ;) first cross over so be…nice?**

 **Disclaimer: I don't own either**

 **Little note: for HoO mine continues from exactly reaching camp... TMI starts from all 6 middle of shadowhunter chronicles so yeah**

* * *

 **The Mortal Instruments Part:**

Clarissa Adele Morgenstern stood with her Stele in her hand. She had no idea when she had picked it up or what she was doing before the time but it had felt important to her. The thought was embedded in her mind and feverishly, she began to draw.

"Clary!" Jonathan Christopher Herondale, or Jace as he preferred to be called, yelled. He had been watching her carefully when he noticed her freeze and automatically, almost robotic, pick up her stele. He tried to move Clary and leave the room but what she had drawn burned red and sparks flew around it. Suddenly they went flying into the unknown.

 *******  
Magnus Bane had heard the commotion coming from Clary's art room in the New York institute. Frowning, Magnus started towards the room but was interrupted by a certain blue-eyed boyfriend.

"Magnus?" called out Alexander Lightwood. Alec was wiping his eyes, a clear indication he had been sleeping. "Wha's goin' on?"

Magnus shrugged and shook his head. As a warlock of his age, everyone expected him to have seen everything and anything otherworldly. This was not true. Magnus, though he'd never admit it, felt as though the younger people knew more than him. He was only here because he was sure Simon had said 9 A.M 13 August... Or was it 18 August? He wasn't sure but he seized the reason the visit his boyfriend.

Magnus held out his hand to Alec and together they went to investigate. Stopping every five steps they finally were in front of Clary's art room, they pushed the door open only to be pulled through the portal-like rune.

 *******  
Simon Lewis and his girlfriend, Isabelle Lightwood arrived at the institute, knowing their friends would be there. Simon felt weird calling Izzy his girlfriend. Don't get him wrong, she's beautiful. One of the most beautiful people he's ever seen. The problem was that Izzy was in love with what he used to be and honestly Simon doesn't remember who that was. He sometimes felt like an idiot, which wasn't his fault, but he felt that way anyway. Izzy had fallen in love with him as a vampire. Obviously he was not one right now but it irked him because he would like to remember. He wanted to know who they, Clary, Jace, Alec, Magnus and especially Izzy, were to him. It wasn't his fault, according to Magnus, he saved their lives in the demon realm but he still felt like a disappointment to them.

Yesterday Simon had gotten permission from the Catarina, the warlock at his school. It wasn't really a school per say, it was a Shadowhunter Academy and he quite liked it, the slimy walls and all. He liked the lessons and he liked when Jace visited and did…whatever Jace wanted to do.

"So you are a nerd?" Izzy asked in confirmation. She tucked a strand of her hair behind her ear and stared at Simon in awe. For the last five minutes Simon had been telling her what he remembered just yesterday. It was memories from his childhood. The way Izzy was looking at him,was almost like Simon could never do wrong by her. She was so strong and emotionless and the only time she dropped the facade was when she was with him alone. She became mushy and just stared at Simon like he was her saving grace.

"Yes. Trust me, Clary and I are obsessed with anime and stuff like that. Speaking of which, where are they?" Finally noticing that Magnus and Alec weren't being all 'lovey' and Clary and Jace were quiet and not arguing about something silly.

Izzy looked around to find Church but then stopped realizing Church wasn't there anymore as Brother Zachariah, Jem, stole their cat. Izzy sulked and shrugged.

"Maybe Clary's art room?" she said softly, still upset about Jem stealing their cat.

"Let's go," he said grabbing her hand and walking to Clary's art room. When the opened the door, they too were dragged to the place of no return. Or so they all hope to prove false.

* * *

 **Camp Half-Blood Part:**

Percy Jackson was tired. It was the second great prophecy he was in. That made him angry. He never wanted to be part of one but he was part of two? What kind of sick joke is this?

The seven now reduced to six went directly to their cabins, except Annabeth who went to Percy's **(A/N: SHH)**. All exhausted but they knew they would have to deal with their adoring fans... Or whatever. They were just tired from fighting Gaia with their parents.

Out of the six, Percy and Annabeth, were the most scarred. During the battle, when they had first come out of Tartarus, there was nothing wrong with them. They basically ignored it but now… they won't be able to. No-one knew of their experience in Tartarus. Percy and Annabeth avoided talking about out but soon the would spill and everyone would know about Percy manipulating poison to kill a Goddess. Everyone would fear Perseus Jackson.

The Olympians didn't really know about Percy and Annabeth's trip to Tartarus but that would probably change soon. The Olympians would also be summoning them soon for glory and wanting to know what happened so fair punishment would be handed out to Hera and Apollo.

Piper, in the Aphrodite Cabin fell asleep as soon as her head hit the pillow.

Hazel and Nico sat across from each other with a dog by the foot of Hazel's bed in the Hades Cabin. They talked about what happened when they separated ways then slept in the early hours of the morning.

Jason, who was still recovering from various head injuries, was in the Zeus cabin fast asleep.

Frank, who often slept in bulldog form, was at the end of Hazel's bed as he truly did not want to go to Ares Cabin as Percy told him Clarisse could be quite mean.

The only Cabin that wasn't really asleep was the Poseidon. Only the ones who knew Percy and Annabeth had fallen into Tartarus, knew they were in the cabin alone. They didn't do anything. Percy just held Annabeth close to him and rocked with her. The gods in Olympus, having noticed this, took pity on them and sent Morpheus, the God of Dreams, to give them peace and let them sleep.

The Demigods did not know that they Would be meeting the Shadowhunters. They did not know Chaos was trying to fix them and Chaos was going to succeed.

* * *

 **I hope you like it**  
 **Review so I know to continue. This story... Is going to be long and hopefully something special**

 **-Katy**


	2. Chapter 2

**HELLO. I'm so sorry for not posting oops… sorry. Thanks for all the reviews and stuff! Hope you like this chapter.**

 **Disclaimer.. I dont own the mortal instruments or Percy Jackson**

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Camp-Half Blood was pretty much in ruins. Every cabin was damaged, and many demigods died. It put a damper on many of the campers but it didn't make them stop. One thing they knew about being children of gods was that you had to learn to move on. Chiron, the camp director was currently calming down Mr D. Zeus had lifted Mr D's banning on alcohol and everyone was going to soon find out that Mr D was a mean drunk (well... Meaner than usual).

The cabin leaders were aimlessly walking around. They were confused and lost. Annabeth wasn't in her cabin and no-one dared wake up Percy Jackson. Even on a normal day Percy had the best warrior reflexes. Something, every camper had known, had happened to Percy and Annabeth. Only the leaders of each cabin knew that it was because they had fallen into Tartarus. Others were kept in the dark. Little did anyone know it wouldn't be for much longer.

"Where are they?" Connor Stoll asked. "It's not like Annabeth to be so late."

Katie nodded. "True but after… you know. Don't you think they need a goodnight sleep?"

Travis smiled at his twin. "Dude chill. Katie's right. They will be-"

A scream cut Travis off. There was a hurricane happening inside camp. There were only two possible people but Jason was with them as the leader of the Zeus/Jupiter cabin.

Jason grimaced. "Percy."

All the cabin leaders ran out towards the Poseidon cabin where they saw the Son of Poseidon on his knees, pulling at his hair. All the campers were watching concerned with what was happening to their leader.

Piper immediately went to him. "Where's Annabeth?" She screamed over the storm.

"Piper! I'm right here. He's...he's having a flashback."

"A flashback of what?" Screamed a camper. "What in the name of Hades could make him act like that?"

Clarisse glared at the offending camper. "Later." She growled.

Annabeth thought of an idea. Albeit a crazy one but it just might work. "Percy? Calm down." She threw herself on him and made him look in her eyes. "I'm right here. I'm not blinded. The Arai are not making your curses come to life. Percy! They can't hurt you! Calm down. Percy, please." She all but whispered the last part.

The hurricane stopped and all the campers were confused. Annabeth blind? Arai? Making curses come to life? When or even where did that happen.

Percy blinked at Annabeth. "Well... Nice way to wake up, right?"

Annabeth huffed. "No."

Nico looked at the two. "What happened to you guys in Tartarus?"

The camp went wild. What? Tartarus?

Nico looked around. "You didn't know? Oh. Oops." He shrugged and Will smirked at him.

"Don't look too happy, di Angelo. You also went to Tartarus."

Nico again shrugged. "Not a big deal, Solace. I'm a son of Hades."

Will scowled. "A son of hades who can't use any of his powers, need I remind you."

Chiron approached Percy slowly. "Are you ready to see the oracle?"

Percy's eyes widened. The oracle? Another prophecy? Are they mad?

"Do I have to?"

Chiron smiled and nodded. "Its good news, I promise."

* * *

Jace Herondale was confused. What the angel happened to Clary and why were they in an actual church. After he and Clary came through that portal, Alec and Magnus came not even a minute later and an hour later Simon and Isabelle. They took stock of what they had and Jace mostly stared at Clary. What happened to her? It just unnerved him so much he couldn't concentrate. She was just so possessed to draw that rune...it was otherworldly. Ethereal.

"So we need info on where we are..."Alec trailed off and exchanged looks with Magnus. Some sort of silent agreement. "We need to spl-"

"We can't do that!" Izzy interrupted. "Seriously. That's like the worst thing we could do. Our phones don't work and clearly none of us have any clue where we are. Don't you think it would be weird to be carrying an unconscious girl throughout the city!"

Jace hid his smile. He did carry said girl through the city... You know after her put that rune on her before he knew she was a shadowhunter. Let's just be happy it worked or Clary would be a forsaken and that would make her boyfriend very sad. She did slap him for it…

"Why don't we split up?" Jace asks. "You know, I'll stay with Clary, Izzy you should go with Alec. And Simon with Magnus."

Izzy looked at Jace surprised. "You want to stay here instead of exploring… Are you okay?"

Jace shrugged. It was unlike him to stay behind but someone had to be with Clary. He smiled at Izzy. "Yeah, Iz. I'm perfectly fine with staying here." Jace looked down dejectedly. He blamed himself. If only he stopped Clary from drawing that rune. If only he was fast enough to realize what happened and stopped her. Obviously he wouldn't have hurt her… but how would he have stopped her. Maybe he should have taken away her stele. Yes, that would have done the trick and they would be home, in the New York institute, happy and safe.

* * *

Alec was confused. Firstly, Clary was unconscious and drew some random rune that took them to another dimension according to Magnus. Secondly, this dimension looked exactly like theirs so honestly Alec was really unsure if they were even in a different place. Sure the institute was now an actual church but other than that this dimension seemed the same. Thirdly Jace stayed behind.

One thing irked him and Magnus – there were no demons.

* * *

"So, we're still in New York?" asked Simon for the umpteenth time.

Izzy sighed. She loved Simon very much but sometimes she wished he would go with the flow. She does that a lot. It's how she doesn't freak out and start to cry hysterically. Add the fact that she's Isabelle lightwood and that she has one hell of a reputation to uphold, she would never be so weak to cry and freak out.

"Si, just go with it for now."

Simon started to pout and stopped. "Iz," he said softly. "Is that boy playing with a…hellhound?"

Izzy started to laugh and turned toward to direction Simon was facing. She stuttered, "I-I believe so."

* * *

 _So this is what I was supposed to do?_ Thought Percy Jackson. _Fine. I'm perfectly okay with that. Mrs o' Leroy is a good hellhound._

Percy smiled to himself. If only all his quests went like this. He looked up and saw a girl and boy watching him with shocked faces. He raised his arm to wave at them but the just watched him intently. Percy reached for his pocket and withdrew a pen, not uncapping it. He waited for them to make the next move. The boy nudged the girl, strode past her towards Percy. Once the boy was in front of Percy, he raised an arm with tattoos to shake. The boy noticed Percy staring at his arm and moved withdrawing a wicked looking glowing knife. "What are you," they both hissed.

The girl laughed. "Boys, there's no need to get feisty." She smiled and introduced herself as Isabelle lightwood and the boy as Simon Lewis. Percy didn't say anything, he just cocked his head and waited for a monster to attack or something like that. He was accustomed to meeting children from other gods after his encounter with Carter Kane and then having to save the world. No big deal in a demigods life.

After 2 minutes where nothing happened but awkward staring Percy finally introduced himself as Perseus Jackson, son of Poseidon…

Simon looked at Isabelle. "So gods exist here. I mean we already know that we aren't in our dimension and I do remember clary telling me something about overlapping… stuff?"

"Yeah, Si. Overlapping stuff. Do you ever listen to anyone?"

Simon contemplated that but before he could say anything Percy interrupted him. "Different dimension? What exists there? I mean in yours."

Simon and Isabelle looked at each other. "We'll explain on the way," Simon said.

Percy wondered is it really a good idea to follow two stranger to a possibly dangerous situation? Probably not but he was going to do it anyway. "Yeah but do you mind if I call my girlfriend? And tell her where we're going?"

Isabelle shrugged. "Since you're taking a leap of faith with us it's only fair we take a leap of faith with you."

* * *

On the way back they found Alec and Magnus making out against the side of a building. Percy was pretty confused when Simon yelled Chairman Meow ran away and the sparkly guy who pinned Alec to the building stopped, started glowing blue and yelled, "Not my cat!"

Percy laughed and thought of Will Solace and Nico di Angelo. Magnus all happiness and sunshine was definitely the son of Apollo and Alec reminded him of Nico all dark and scary but still nice in a way.

Magnus looked at Percy. "Who's that?"

"I'm Percy but honestly if there are more of you guys can I say it all one time?"

Magnus shrugged and Percy noticed his cat eyes. "why do you have cat eyes?"

"I'm a warlock."

"Why don't they have cat eyes?" he pointed at the others.

"We're Shadowhunters." Alex said. "We come from a dimension of angels and demons." Alec turned to his sister. "Where did you even find this guy?"

Simon smiled. "He was petting a hellhound."

Alec frowned. "And where is said hellhound?"

Percy spoke up this time. "Mrs o' Leroy ran away from Simon. Guess she didn't like you that much."

Alec looked at Magnus and smiled. "I like this guy."

* * *

As soon as they walked into the church, Magnus went to go check on Clary as Jace want to go see the new guy. Apparently they're in a world where Greek gods exist. Also Roman an-

"Is Magnus talking to himself?" Izzy asked but Jace was already gone checking on Clary.

* * *

Clary woke up with a painful headache. She had no idea where she was or what had happened before. She looked up and opened her eyes, staring directly into Magnus's cat eyes.

"Hey, Biscuit. How are you doing?" he asked concernedly. He always loved Clary even though as a toddler she had pulled Chairman Meow's tail. It was a big deal because everyone knew that if it came down to saving Alec or the cat, Magnus would have a very difficult decision to make.

Clary rubbed her eyes. "I don't..." She trailed off looking around. Her surroundings looked familiar yet odd. She was in a church pew, no longer in her art room. She couldn't figure out why she was here and it did look a little familiar. With a jolt, she remembered being almost possessed with the need to draw a Rune. And that Rune did... something. As a Shadowhunter one thing Jace drilled into her head was that she should follow her instincts. "Are we in New York?"

Magnus nodded then hesitated. "We are in New York, Alright, only problem is that we aren't in our own dimension. Somehow you managed to open a portal to a new dimension. One directly parallel to ours with over lapping properties but instead of demons and Shadowhunters, there are gods and monsters."

Clary raised her brows. Magnus was a warlock but how was it possible her knew that much?

"Clary?" Jace asked. "Are you alright? You haven't missed a lot just our..." He trailed off as a black-haired boy popped his head in.

"I don't think we're friends, yet," said the boy. Jace nodded at the boy, acknowledging the truth in that sentence. The boy shook his head, looked at Clary and said, "Where are my manners? Hi, my name's Perseus Jackson, Son of Poseidon, but please call me Percy."

* * *

 **I will update real soon. Thanks and stuff**

 **Ps:**

 **Mustloveherondalemen:** Aww I hoped you like it

 **Margarita P (guest):** Will do! I love both books as well.

 **Rose Hathaway (guest):** obv. it has spoilers its after both series! Sorry Rose!

 **Guest:** Will do. I can't wait to show you what happens!

 **Arandomfangirler:** HAHA I see what you did there.. awesome

 **Black Bankai:** Thanks! I was kinda worried it might be bad..

 **Hailey Face:** Thank you so much!

 **-Katy**


	3. Chapter 3

**Disclaimer: I don't own Jace or Persassy and this will probably be the bane of my existence.**

* * *

"So, what do we do now?" Simon said as he looked at Izzy. The gang listened intently to what Percy had said. Greek gods… Roman gods and lots of quests.

Percy smiled, "I have no idea why you guys are here… maybe we should go to Olympus and ask the gods if they summoned you?"

Simon thought that wasn't such a bad idea. Before he could say anything, the door of the church opened and a girl with curly blond hair stood stoically. "Perseus Jackson! How could you leave me! Going with a bunch of random strangers? Are you mad? No offense to you guys it's just that we don't know who you are and-," she let out a frustrated groan. Simon could now see that she was truly panicking without Percy. Percy looked at her calmly almost as if he'd been in this situation many times before. Simon could easily imagine that. Percy looked like a trouble maker.

"Annabeth, babe. Come on! I sent you a message and," he sighed. "I'm sorry."

"Okay… Just don't do that again."

Percy smiled. "Never again."

Annabeth eyes filled with tears and looked down. "It's what he said right before we fell into Tartarus."

The 6 people behind Annabeth looked solemn. To be honest Simon had not noticed them until now and that was bad. As a Shadowhunter in training, he should have noticed them and classified them as threats. Simon thought about what she said. Tartarus? Wasn't that like hell or a demon realm?

"Percy!" said the blond wearing a superman t-shirt, standing beside Annabeth. "Bro… We didn't even leave you alone for an hour and you make new friends?"

Percy smiled and said, "Bro, I'm like a puppy – always happy and making new friends."

Izzy smiled. "We literally met him 15 minutes ago. He was petting a hellhound, which if I can say is pretty damn weird."

Percy and Annabeth burst out laughing. Simon looked at them weirdly and noticed he wasn't the only one. Everyone just stared at them and shook their head like they knew they wouldn't get the joke.

"Okay, why don't we introduce ourselves?" Jace said finally. It was amazing that he was quiet for so long but Simon had noticed him talking to Clary. He really loved Clary and she was always his first priority, even if the world was burning. It was the same for her. As long as she had him, it didn't matter what she owed heaven or hell. Simon shook his head. That was...familiar. Eerily familiar and creepy.

"Jason Grace, Son of Zeus… I guess. I'm his roman's form child." Jason shrugged.

"Piper Mclean, Daughter of Aphrodite." The girl smiled. She had a nice voice.

"Frank Zhang, Legacy of Poseidon, son of Ares or Mars." He smiled very timidly.

"Hazel Levesque, Daughter of Pluto or Hades?" the girl smiled warmly. She was adorable.

"Will Solace, Son of Apollo." He looked at the boy next to him. "The grumpy one is my boyfriend Nico di Angelo, Son of hades."

The girl that yelled at Percy said. "Annabeth Chase, daughter of Athena. " She looked at her boyfriend. "And that puppy, I'm sure you know him, Perseus Jackson, Son of Poseidon."

Perseus sighed. "Call me Percy."

"I'm Simon lewis. A Shadowhunter."

"Isabelle lightwood. Same as him."

"Jonathon Christopher Herondale. Call me Jace. Also Shadowhunter. The tired person on my lap is Clarissa Morgenstern." His girlfriend hid her face and punched Jace in the stomach. "Call her Clary."

"Just don't call her biscuit that's my thing. I'm Magnus bane-"

"You have the same name as my cousin, Magnus Chase." Annabeth stated

Magnus pouted. "You ruined my dramaticness. I'm Magnus Bane, High warlock of Brooklyn. Uhm. I'm forgetting something. Oh yes!" glitter exploded and Magnus smiled happily. "That's my boy toy Alexander -Alec- lightwood, he's a sexy Shadowhunter." Alec blushed at that remark.

"Magnus! Do you have to be so-"Alec stopped and stared at something behind Magnus. Everyone looked and saw what he stared at.

A crash sounded and bright light suddenly appeared. Simon looked and couldn't believe his eyes. The air rippled and deposited something. A greenish-grey blob with a glowing black core **(A/N I'm literally sitting here with my Shadowhunter codex… mwahahah).** Simon took a closer look and it clicked.

A du'sien

* * *

Percy was used to weird things happening but this… was probably in the top 5. The greenish-grey blob started to move and form actual limbs. Perhaps its journey here was a rough and tumble so it didn't have a form? Percy didn't particularly care but it was a little too close to Clary and she looked a little dazed. He reached to get riptide but then stopped. This thing- whatever it was- wasn't from his dimension so could celestial bronze destroy it? Percy didn't know and wasn't going to find out because in one strike it was gone and Jace was smirking lazily, tossing a blade and catching it.

"That was easy," Jace said and looked at Clary who turned and beamed at her boyfriend.

"It was a du'sien demon. You know the lesser known to the eidolon demon, but Jace is right. That thing didn't even get to form before it was killed. If it was a facemelter then things would-" Simon was abruptly interrupted by Jason.

"Wait. You have a demon named facemelter?"

Jason's girlfriend, Piper, elbowed him. "We just saw a demon and the weirdest thing for you is the name?"

"Didn't you here what Simon said! He said it's a du'sien demon not a facemelter which would be more dangerous," Izzy said getting a little angry.

Jason being the peace keeper held up his arms in a T. Just before he could say anything, the Shadowhunters and demigods were…gone.

* * *

 **So short... Jammer but I had to end it there..the rest is just like totally for another chapter!**

 **Will update real soon!**

 **-Katy**


	4. Chapter 4

**Sorry for the long wait, guys. Exams... It's almost over..3 left ㈳5**

 **Everything is owned by Riordan and Clare**

 **Chapter 4**

* * *

"Uhm..." Nico began, "Lord Zues, no offense but that was a bad idea considering those two..." he pointed to Annabeth and Percy standing back to back, looking angry.

Percy smirked and said, "You think we're bad? Look at the shadowhunters!" The shadowhunters were armed with wicked looking knifes in each arm except; Clary-who held a glowing stick(how was that going to help?)-and Magnus who looked at Percy with on eyebrow raised. "And the warlock." Percy quickly amended.

Zues looked confused. "I did not summon you."

"Cool," Simon said. "So these are the gods? That's so-"

"No, he did not summon you, I did." Said a guy dressed in a black duster. It moved as if it was made of smoke.

Magnus sighed. "Don't worry, my dramatic introduction was also ruined."

"But that was completely different! This one was, I'm guessing-"

"Oh no! Jason's guessing."

Jason glared at Piper before continuing. "As I was saying, probably due to a miss calculation but Magnus' was due to Annabeth interrupting."

The guy cleared his throat. "Do you want me to continue or..." He looked around skeptically. "I am Chaos, Creator of the universe. I shant make this long, but first if I could get you all to lower your weapons."

The demigods didn't hesitate to sheath their weapons but the shadowhunters and warlock were more skeptical.

Percy smiled. "Do you guys trust us?"

Jace smirked. "Not really but do we have any choice?" The shadowhunters sheathed their weapons except clary who just twirled the sticky thingy. **(A/N know it's a stele they don't!)**

Chaos smiled. It was pretty creepy considering he looked ageless and his eyes were pretty mesmerizing. They literally were everything- the stars and millions of galaxies, everything. "I hope you are all ready for an adventure of a life time." He winked at Magnus. "Yes, even yours of an immeasurable amount of time.

"As you know, you are here to due a tear in the dimensions iota and eta **(A/Nyes i just used greek letters... Totally made up the dimensions though)**. Iota being this one and the others yours. I cannot help much but I can tell you there are 13 tears with iota and eta." He looked thoughtfully into the sky. "At each one a there is a demon of some sort - i do not know what but its there. Its your duty to destroy them and repair the tear - I'm sure Clary will come up with something to fix it.

"I'm sorry, but i cannot stay longer. It drains me to be in this form," with that he said he vanished.

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 **And thats a wrap. The next update will be soon I promise... I was going to say something... Uhm... Oh yes review but mainly follow so i know people actually care ㈏3㈏3㈏3**

 **This is so short.. I will update REALLY SOON due to the short chapter**

 **Love**

 **Katy**


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